Method and apparatus for continuous soapmaking



Dec. 20, 1955 F. T. PALMQvlsT METHOD AND APPARATUS FOR CONTINUOUS SOAPMAKING 3 Sheets-Sheet l Filed Jan. 2, 1951 IIIJ;

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Av- TORNEYS Dec. 20, 1955 F. T. PALMQVIST METHOD AND APPARATUS FOR CONTINUOUS SOAPMAKING 3 Sheets-Sheet 2 Filed Jan. 2, 1951 mm .mm il ATTORNEYS Dec. 20, 1955 F. T. PALMQvlsT METHOD AND APPARATUS FOR CONTINUOUS SOAPMAKING 3 Sheets-Sheet 3 Filed Jan. 2, 1951 Maf A TTozA/.Lrys

nited States Patent O IVIETHOD AND APPARATUS FOR CONTINUOUS SOAPMAKING Fredrik Teodor Palmqvist, Stockholm, Sweden, assignor to Aktiebolaget Separator, Stockholm, Sweden, a corporation of Sweden Application January 2, 1951, Serial No. 203,840

13 Claims. (C1. 2150-418) This invention relates to a method and apparatus for the continuous manufacture of soap, in which the material is subjected to a series of successive operations.

The manufacture of soap in a continuous process is not novel in itself, but known methods devised in recent years have certain inconveniences, which it is an object of the present invention to overcome.

In the conventional manufacture of soap, the procedure is briey as follows: F at and lye are saponitied, and the product obtained is grained out with a salt solution, usually common salt, whereupon the neat soap thus formed is separated from the spent lye and then washed, in a tting stage, with lye and salt solution, a purified soap thereby being obtained after removal of the new spent lye or the niger.

The present invention differs from the known methods with regard to the manner in which the various stages are carried out.

It is known that when saponifying fat with lye the reaction at first takes place slowly, until a certain amount of fat has been saponilied, and then suddenly proceeds at a very high rate which then diminishes. Thus, the time-saponication curve is similar to an S. This fact is utilized in the present invention.

A characterizing feature of the present invention is that, after continuity of operation has been reached, saponied fat is kept in continuous circulation in a separate circuit in the first or saponication stage, and lye is added at a suitable point of the circuit in order to saponify non-saponied fat (if any) and fat difficult to saponify, as well as fat fed to this circuit. The lye and fat are continuously added in fixed proportions and thoroughly mixed or atomized in the circulating material, and a quantity of saponied fat corresponding to the added quantity is continuously withdrawn from the circuit and fed to the next stage.

Another feature of the invention is that the grainingout stage following the saponifying stage isfully separated from the latter and likewise provided with a circuit to which predetermined amounts of a salt solution are continuously fed while a portion of the circulating material is continuously withdrawn. This withdrawn material is led into a centrifugal separator where it is separated into a stream of neat soap, which is fed to the subsequent fitting stage, and a stream of spent lye containing traces of soap together with glycerol, salts and organic compounds, which are withdrawn from the process.

A third feature is that the neat soap is washed in one or several (usually two) successive fitting stages, each of which is preferably provided with a circuit to which neat soap, lye and salt solution are fed and from which a stream of the material is continuously withdrawn into and separated in a centrifugal separator. When two consecutive fitting stages are used, the neat soap from the separator of the first tting stage is fed, together with lye, salt solution and water, to the circuit of the second tting stage, and the niger discharged from the separator of the second tting stage and consisting of lye, salt solution, soap and water is returned to and used in the circuit of the first tting stage.

A fourth feature is that the saponifying and graining stages and, if required, the tting stage or stages may be carried out at superatmospheric pressure, which makes it possible to use a raised temperature. The effect of the raised temperature is to shorten the saponifying time, to lower the viscosity of the material, resulting in increased throughput of the separators, and to reduce the water content of the grained-out soap, which facilitates the subsequent iitting or pitching operation. When the saponifying stage is effected at elevated pressure and elevated temperature, this part of the installation can be made smaller owing to its increased capacity. When the saponifying and graining stages, and possibly the tting stage or stages, are effected at elevated pressure, an advantage is obtained in that the dosing or metering devices used for the supply of fat and lye (and, if required, salt solutions and water) to the circuits of the various stages, may be made as propelling devices for passing the soap mass through the whole or a part of the system, in which case they preferably consist of piston pumps. One or several of the pumps otherwise required in the pipes to the separators may then be eliminated. When elevated pressure is used, the separators should be of the air-tight or closed type.

For a better understanding of the invention reference may be had to the following description in conjunction with the accompanying drawings, in which Figs. l, 2 and 3 are diagrammatic views of three different forms of the new apparatus adapted for use in practicing the method of the invention.

In Fig. l I have illustrated a saponifying stage, a graining stage, and two fitting stages. The last fitting stage is not always necessary and may be eliminated.

The apparatus of the saponification stage comprises a tank or holding zone 1, a circulation pump 2, a tank or holding zone 3, a mixer 4, and a heater 5, communicating with one another through pipes 6, 7, 8, 9, 10 and 11, and forming together the circuit of the saponifying stage. The fat to be saponiied is supplied through pipe 12 and the lye through pipe 13. in continuous operation, part of the material is withdrawn through pipe 14 to the next stage. The fat is generally in luid form and the lye, usually sodium lye, is relatively strong. Before starting the plant, the pipe 14 is preferably closed by a valve 14a, whereupon fat and lye in accurately controlled amounts are continuously fed into the circuit through pipes 12 and 13, as by metering or dosing devices such as piston pumps, and are circulated by' the pump 2. The mixture is heated in passing through the heater 5, which may be of any conventional type. The temperature should be suiciently high to allow the soap to be pumped, but it may exceed C. When the saponication takes place at a temperature higher than 100 C., the apparatus must be constructed to withstand the generated high pressure. After a period of feeding and circulation, with valve 14a closed, the tank 1 will be lled to a certain level and contain mainly saponiiied fat. The valve 14a is then opened and a stream containing a minor portion of the saponilied fat is led through pipe 14, the major portion continuing to pass through the circuit while lye and fat are added thereto in xed proportions. The lye added in front of the pump Z saponies any residual fat or fat dicult to saponify in the stream arriving from tank 1, the pump effecting a good mixing action so that the lye reacts with the soap in tank 3 to form an alkaline soap emulsion, to which fat is then added through pipe 12. Because the alkaline soap emulsion already contains a completely saponiiied fat when the addition of fat is made through pipe 12,'the saponiiication of the added fat takes place more rapidly than if no soap were present. The saponication is facilitated by passing the material through the mixer or mixing zone 4, which produces an emulsion of fat and alkalne soap, and by the heating in the heating zone 5. As the saponifying reaction is exothermic, the heater may, if required, be turned olf during continuous operation. The soap discharging in continuous operation from tank 1 has been practically completely saponied therein. Owing to the continuous circulation in the saponifying circuit, it is possble to add the fat yand lye through dosing or metering devices in the form of piston pumps, whereby they become evenly distributed in the mass by the circulation. The tank 1 has a small diameter in relation to its height, fory the purpose of making the mass pass evenly through it.

The apparatus of the graining stage comprises a circulation pump 15, a tank 16, and communication pipes 17, 18 and 19, all of which form the circuit of the graining stage. This stage also comprises a feed pump 20, a centrifugal separator 21, pipes 22, 23, 24, 25 and also a pipe 26. Saponied material from the saponifying stage is fed to the circuit of the graining stage through the pipe 14, and a salt solution, generally containing ordinary salt, is added through pipe 26 from a dosing or metering device (not shown). Owing to the circulation in the graining circuit, a piston pump may also be used to advantage here as dosing device. The mixture is circulated through the graining circuit by the pump 15, and a part is discharged to the separator 21 through the pipe 22. The added salt solution should be of optimum quantity and concentration. After the material has passed through the separator 21, neat soap is obtained as one of the separated components in discharge pipe 25 and is led to the tting stage or stages. The other separated component, comprising glycerol, small amounts of soap, salts and possibly organic impurities, is discharged through pipe 24 and withdrawn from the process. If required, a heating device (not shown) may be arranged in pipe 17.

The first iitting stage also includes a circuit, comprising a circulation pump 27, a heater 28, a tank 29 and communication pipes 30, 31, 32, 33, and also a feed pump 34, a centrifugal separator 35 and pipe lines 36, 37, 38, 3 9 and 40. Neat soap is fed. to this circuit through pipe 25, and lye and salt solution through pipe 40. The mixv ture of Athese materials is pumped through the iirst tting circuit by the pump 27 and is heated in the heater 28. Only a part of the circulating stream is Withdrawn through pipe 36 into the separator 35. Lye and salt solution are preferably added through pipe 40 by a piston pump as the dosing or metering device. Neat soap is discharged from .the separator 35 through the, pipe. 39 and is further reared` in the second fitting stage, if there is any such stage. The other component separated in the centrifuge 35, which is niger consisting of a mixture of salts, soap and water, is dischargedV through the pipe 38. These products may be re-introduced into the process, as will be described in the following.

The second fitting stage has also a circuit, comprising a circulation pump 41, a heater 42, a tank 43, and pipes 44, 45, 46, 47, and also a feed pump 48, a centrifugal separator 49, and pipes 50, 51, 5.2, 53, 54. Neat soapis introduced into the circuit of the second tting stage through pipe 39, and lye, salt solution and water through'V pipe 54, and are circulated by the pump while being heated in the heater 42. Only a small portion of the circulating mixture is withdrawn through pipe 50 and separated in the separator 49, from which soap mass discharges through y c device for introducing lye, salt solution and water into the system through the pipe 54.

The niger discharging through pipe 3S in the rst tting stage may advantageously be reintroduced into the process, either wholly or in part, depending upon its cornposition. If required, it may first be purified in container 38a. its alkali and salt contents may also be adjusted in container 38a by adding caustic soda, salt or water. The substances may be introduced into the circuits of the saponifying or graining-out stages, as indicated by dash lines in the drawings.

As compared with prior methods for continuous soapmaking, the invention has the advantage of giving a practically complete saponiiication in a single stage, which is made possible because the niger is subiected to the action of lye in great excess during one phase of the process in the circuit. Another advantage is quick emulgation of the fat because it is pumped into niger. The saponitication therefore starts on the steep part of the time-saponitication curve, so that the saponitication period becomes comparatively short. In other words, previously formed soap mass is utilized to accelerate the saponiiication, which, so far as I am aware, is a new principle in this art. In addition, the power consumption is lower than in most other processes for the same purpose, owing to the good fat-emulgating properties of the niger. The saponiiication heat is utilized to obtain better thermal economy, which is novel in conjunction with the circulation through the circuit of the saponification stage. The method also has the advantage of enabling a small total excess of lye, which means saving of lye as well as Work and expense necessary to neutralize excess lye, all inconveniences inherent in other similar methods. By using a circuit in one or more of the various stages, any fluctuations in the dosing of substances added in the process are equalized, rendering it possible to use low speed piston pumps as dosing devices, which is advantageous to their reliability. By using holding 'tanks in the circuits, the circulating soap mass may be observedv and supervised. Particular advantage is ascribed to the fact that the niger is grained-out in a separate stage, independent of the saponifying stage, so that the graining operation does not interfere with the saponitication. This makes it possible to use the optimum quantity and concentration of salt. The presence of salt in the saponifying stage may cause incomplete saponification. 'When the fitting is effected in two stages, the niger phase discharged at 52 from the second stage may advantageously be returned to the iir'st iitting stage. The method also has the advantage that not more than two or three centrifugal separators are required, which is less than with other comparable processes. The pumps 2, 15, 27 and 41 also serre as mixing devices.

The installation illustrated inFig. 2 diiters from that of Fig. 1 only in certain respects, and the same reference numerals have therefore been used for corresponding parts in both illustrations. The dierences between the two installations are set forth below.

The installation of Fig. 2 Ais intended for operation at elevated or super-atmospheric pressure and, if required, elevated temperature in the saponication and grainingout stages, whereas the iitting stages are effected at atmospheric pressure. The numerals 6i), 61 and 62 denote dosing pumps (for example, of the piston type) for feeding fat, lye and salt solution into the pressure stages. Consequently, these pumps must Work with elevated pressure, and lthey can advantageously be used for forcing vthe soap through the steps of the iirst two stages. The

feed pump 20 illustrated in Fig. 1 can thus be dispensed with which means a simplification of the installation. Fig. 2 shows a heater 63 in pipe 17 and also shows a pump 64 (for example, a piston pump) which is necessary to force the niger fromV pipe 38 into the pressure stages through the pipes 65 or 66, after adjustment of its concentration and, if required, purification. The dosgnam ing devices used for pipes 40 and 54 are not shown, as they may be of any conventional type.

The installation of Fig. 3 works entirely at elevated pressure. Although two fitting stages are shown, one is sometimes sufficient. This installation differs only Very little from that of Fig. 2, and the reference numerals used in Fig. 2 apply in Fig. 3 for corresponding parts. The difference between Fig. 2 and Fig. 3 lies in the execution of the fitting stages. Between the graining stage and the first fitting stage, in Fig. 3, there is a tank 67 in which the pipes 25 and 40 and, if required, the pipe 56 end. The lye and the brine are preferably introduced by means of a dosing device 68 acting as a piston pump. A pipe 70 provided with a pump 69, preferably of the piston type, runs from the tank 67 to the circuit of the first tting stage. This arrangement makes the pump 34 of Fig. 2 superfluous. Between the first and the second fitting stage there is also a tank 71 in which the pipe 39 from the separator of the first fitting stage and the'pipe 54 for supply of lye, brine and water end. The latter pipe is provided with a pump 72, preferably of the piston type, as a dosing device. A pipe 74, preferably also provided with a pump 73 of the piston type, extends from the tank 71 to the circuit of the second tting stage. The feed pump 48 of Fig, 2 may then be eliminated.

The embodiments illustrated and described as examples are shown only diagrammatically and for this reason various control valves desirable in such apparatus have not been shown in the drawings.

I claim:

1. In the manufacture of soap by a continuous process in which the soapmaking material is passed through a plurality of consecutive stages, the improvement which comprises continuously circulating saponifiable material at least partly saponified in a separate circuit in a saponification stage, feeding saponiable material to be saponified into the circuit, feeding a saponifying agent into the circuit at a point in advance of the point at which said saponifiabie material is fed into the circuit, reckoned in the direction of fiow through the circuit, to saponify any circulating non-saponified material and material difficult to saponify as Well as said saponifiable material fed into the circuit, the saponifying agent and saponiiiable material being introduced continuously into the circuit in predetermined portions and atomized in the circulating material, passing the saponied material through a holding zone on its way from said point of the saponifying agent feed to said point of the saponifiable material feed, and withdrawing from the circuit and passing to the next stage saponified material at a rate corresponding approximately to the rate of feeding to the circuit, the saponified material being withdrawn from the circuit at a point thereof located beyond said point of the saponiliable material feed and in advance of said point of the saponifying agent feed, reckoned in said ow direction.

2. The improvement according to claim l, comprising also the steps of accumulating in a second holding zone a mass of circulating saponified material in the circuit prior to the withdrawal of saponified material at said rate, and, during said accumulation and circulation, passing the saponiiiable material and saponifying agent fed into the circuit through a mixing zone therein to mix them intimately togetherv and thence through a heating zone in the circuit to heat the mixture and thereby accelerate the saponication.

3. The improvement according to claim l, comprising also the steps of accumulating in a second holding zone a mass of circulating saponified material in the circuit prior to the withdrawal of saponiiied material at said rate, and, during said accumulation and circulation, passing the saponifiable material and saponifying agent fed into the circuit through a mixing zone therein to mix them intimately together and thence through a heating zone in the circuit to heat the mixture and thereby ac- Celerate the saponification, and reducing the supply of 6` heat to the mixture in said last zone upon completion of said accumulation and attaining continuity of operation.

4. Ihe improvement according to claim 1, in which the saponifying agent fed into the circuit is strong lye.

5. The improvement according to claim 1, in which, during the circulation in said circuit, complete saponification of the saponiable material is effected at said holding zone to form an alkaline soap mass, said saponifiable material to be saponir'ied being combined with the alkaline soap mass leaving the holding zone and mixed therewith in a mixing zone, whereby said saponifiable material is quickly saponified due to its content of soap, the material passing from the mixing zone through a second holding zone from which a part of the material is led to said next stage While the remainder continues to circulate in said circuit.

6. The improvement according to claim l, comprising also the steps of feeding into a separate circuit in a graining stage saponified material thus withdrawn from said first circuit, feeding a salt solution into the graining circuit while circulating saponified material therein, continuously discharging from the graining circuit part of the material circulating therein, said last part being discharged from the graining circuit at a point thereof l0- cated beyond the point at which said saponilied material is fed thereto and in advance of the point at which the salt solution is fed thereto, reckoned in the direction of iiow through the graining circuit, continuously centrifuging said discharged part to separate it intoa phase including traces of soap and glycerol, salts and organic impurities and a second phase consisting mainly of a soap mass, and passing the soap mass to the next stage.

7. The improvement according to claim 1, comprising also the steps of feeding into a separate circuit in a graining stage saponied material thus withdrawn from said first circuit, feeding a salt solution into the graining circuit while circulating saponified material therein, continuously discharging from the graining circuit part of the material circulating therein, said last part being discharged from the graining circuit at a point thereof located beyond the point at which said saponied material is fed thereto and in advance of the point at which the salt solution is fed thereto, reckoned in the direction of flow through the graining circuit, continuously centrifuging said discharged part toseparate it into a phase including traces of soap and glycerol, salts and organic impurities and a second phase consisting mainly of a soap mass, feeding said soap mass into a separate circuit of a fitting stage, feeding lye and a salt solution into the fitting circuit while circulating the soap mass therein, continuously discharging from the fitting circuit part of the mass circulating therein, said last part being discharged from the fitting circuit ,at a point thereof located beyond the point at which said soap mass isl fed therein and in advance of the point at which the lye and salt solution are fed therein, reckoned in the direction of liow through the fitting circuit, and continuously centrifuging said last part to separate it into a niger phase and a soap phase.

8. The improvement according to claim 7, comprising also the steps of feeding the soap phase from said last centrifuging into a second fitting circuit, feeding lye, salt solution and water into the second fitting circuit while circulating the Soap phase therein, continuously withdrawing from said last circuit part of the material circulating therein, said last part being withdrawn from the second fitting circuit at a point thereof located beyond the point at which said last soap phase is fed thereto and in advance of the point at which said lye, salt solution and water are fed thereto, reckoned in the direction of flow through the second fitting circuit, and continuously centrifuging said last part to separate it into a niger phase and a soap phase.

9. The improvement according to claim l, comprising also the steps of feeding into a separate circuit in a graining stage saponied material thus withdrawn from said 7 first circuit, feeding a salt solution into the graining circuity while circulating saponied material: therein,v continuously discharging from' the graining circuit part of the material circulating therein, said4 last part being discharged from the graining circuit at a point thereof located beyon-d the point at which said saponified material is fedi thereto andv in advance of the point at which the.

salt solution is fed thereto, reckoned in the direction of fioW through the graining circuit, continuously centrifuging said dischargedv part to separate it into a phase including traces of soap and glycerol, salts and organic impurities and a second phase consisting mainly of a soap mass, feeding said soap mass into a separate circuit of a fitting stagefeeding lye and a salt solution into the fitting circuitv while circulating the soap mass therein, continuously discharging from the fitting circuit part of the mass circulating therein, said last part being discharged from the fitting circuit at a point thereof located beyond the point at which said soap mass is fed therein and in advance of the point at Which the lye and salt solution are fed therein, reckoned' in the direction of ow through the fitting circuit, continuously centrifuging said last part to separate it into a niger phase and a soap phase, and returning at least partv of said niger phase to one of said circuitsl in advance of thev fitting circuit.

10. The improvement according to claim l, `comprising also the steps of feeding into a separate circuit in a graining stage saponified material thus withdrawn from said first circuit, feeding a salt solution into the graining cir cuit while circulating saponified material therein, continuously discharging from the graining circuit part of the material circulating therein, said last part being discharged from the graining circuit atv a point thereof located beyond the point at which said saponified material is fed thereto and in advance of the point at which the salt solution is fed thereto, reckoned in the direction of flow through the graining circuit, continuously centrifuging said discharged part to separate it into a phase including traces of soap and glycerol, salts and organic impurities and a secon-d phase, consisting mainly of a soap mass, feeding said soap mass into a separate circuit of a fitting stage, feeding lye and a salt solution into the fitting circuit while circulating thesoap mass therein, continuously dischargingfrom the fitting circuit part of the mass circulating therein, said last part being discharged from the fitting circuit at a point thereof located beyond the point at which said soap mass is fed therein and in advance of the point at which the lye and salt solution are fed therein, reckoned inv the direction of flow through the fitting circuit, continuously centrifuging said last part to separate it into a niger phase an-d a soap phase, feeding said last soap phase into a second fitting circuit and there mixingit withrlye, salt solution and water while circulating the soap phase thereon, continuously withdrawing from said last circuit part of the material circulating therein, said last part being `withdrawn from the second fitting circuit at a point thereof located beyond thel point at which said last soap phase is fed thereto and in advance of the point at which said lye, salt solution and water are fed thereto, reckoned in the direction of flow through the second fitting circuit, continuously centrifuging said last part to separate it into a niger phase and a soap phase, and returning atA least Ypart of said last niger phase to said first fitting circuit.

ll. The improvement according to claim 1, in which first. circuit, feeding a salt solution into the graining cir-L cuit while circulating saponified fat therein, continuously discharging from the graining circuit part of the material circulating therein, said last part being discharged froxn the graining circuit at a point thereof 1ocated beyond the point at which said saponified material `is fed thereto and in advance of the point at which the salt solution is fed thereto, reckoned in the direction of fiow. through the graining circuit, continuously centrifug- .ing said discharged part to separate it into a phase including traces of soap and glyceroL, salts and organic impurities and a second phase consisting mainly of a soap mass, and passing the soap mass to the next stage, the material being maintained under superatrnospheric pressure in the saponification and graining stages, to permit elevated temperature therein.

13. The improvement according to claim l, comprising also the steps of feeding into a separate circuit in a graining stage saponied material rthus Withdrawn from said first circuit, feeding a salt solution into the graining circuit while circulating saponified fat therein, continuously discharging from the graining circuit part of the material circulating therein, said last part being discharged fromrthe graining circuit at a point thereof located beyond the point at which said saponified material is fed thereto and in advance of the point at which the saltA solution is. fed thereto, reckoned in the direction of dow through the graining circuit, continuously centrifuging said discharged part to separate it into a phase including traces of soap and glycerol, salts and organic impurities and a second phase consisting mainly of a soap mass, feeding said soap mass into a separate circuit of a fitting stage, feeding lye and a salt solution into the fitting circuit while circulating the soap mass therein, continuouslyV discharging from the fitting circuit part of the mass circulating therein, said last part being discharged from the fitting circuit at a point thereof located beyond the point at which sai-d soap mass is fed therein and in advance of the point at which the lye and salt solution are fed therein,` reckoned in the direction of flow through the fitting circuit, and continuously centrifugingl said last part to separate it into a niger phase and a soap phase, the material being maintained under superatmospheric pressure in said saponifying, graining and fitting stages, to permit elevated temperature therein.

References Citediin the file of this patent UNITED STATES PATENTS 

1. IN THE MANUFACTURE OF SOAP BY A CONTINUOUS PROCESS IN WHICH THE SOAPING MATERIAL IS PASSED THROUGH A PLURALITY OF CONSECUTIVE STAGES, THE IMPROVEMENT WHICH COMPRISES CONTINUOUSLY CIRCULATING SAPONIFIABLE MATERIAL AT LEAST PARTLY SAPONIFIABLE MATERIAL TO BE SAPONIFICATION STAGE; FEEDING SAPONIFABLE MATERIAL TO BE SAPONIFIED INTO THE CIRCUIT, FEEDING SAPONIFIABLE AGENT INTO THE CIRCUIT AT A POINT IN ADVANCE OF THE POINT AT WHICH SAID SAPONIFIABLE MATERIAL IS FED INTO THE CIRCUIT, RECKONED IN THE DIRECTION OF FLOW THROUGH THE CIRCUIT, TO SAPONIFY ANY CIRCULATING NON-SAPONIFIED MATERIAL AND MATERIAL DIFFICULT TO SAPONIFY AS WELL AS SAID SAPONIFIABLE MATERIAL FED INTO THE CIRCUIT, THE SAPONIFYING AGENT AND SAPONIFIABLE MATERIAL BEING INTRODUCED CONTINUOUSLY INTO THE CIRCUIT IN PREDETERMINED PORTIONS AND ATOMIZED IN THE CIRCULATING MATERIAL, PASSING THE SAPONIFIED MATERIAL THROUGH A HOLDING ZONE ON ITS WAY FROM SAID POINT OF THE SAPONIFYING AGENT FEED TO SAID POINT OF THE SAPONIFIABLE MATERIAL FEED, AND WITHDRAWING FROM THE CIRCUIT AND PASSING TO THE NEXT STAGE SAPONIFIED MATERIAL AT A RATE CORRESPONDING APPROXIMATELY, TO THE RATE OF FEEDING TO THE CIRCUIT, THE SAPONIFIED MATERIAL BEING WITHDRAWN FROM THE CIRCUIT AT A POINT THEREOF LOCATED BEYOND SAID POINT OF THE SAPONIFIABLE MATERIAL FEED AND IN ADVANCE OF SAID POINT OF THE SAPONIFYING AGENT FEED, RECKONED IN SAID FLOW DIRECTION. 